HELP Balloon Frame Sill replacement

Hi,
It seems like I have hit a major obstacle with the repair of my sill in a balloon frame construction 1920s bungalow (2 floors). The rear foundation sill is completely rotted out – about 30 feet. My understanding of balloon construction is that the floor joists and the wall studs are “separate†and that jacking up the floor basically has no impact on the wall; the wall would have to be supported independently. <!—-><!—-><!—->
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Here’s the problem: an engineer has drawn up plans to support the wall by spanning from the outside to the inside (perpendicular to the foundation) – I believe with a steel “channel†bolted to each stud. The contractor doesn’t want to do it this way, he wants to shoring the wall from the outside, using 2x6s or 2x8s at a 45 degree angle, similar to supporting a porch. The engineer states that because this is balloon construction, the contractors method will merely push in the wall, not really supporting it. They have spoken and are at a stand off.<!—-><!—->
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Has anyone dealt with this problem? I can’t tell if the engineer’s method is theory that no one can execute or if the contractor does not really understand the physics going on.<!—-> <!—->
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All opinions very welcome. Thanks in advance! Joe Joyce, <!—-><!—-> <!—->Boston<!—-> <!—->MA <!—-><!—-><!—-> <!—->